"Non leggo il libro, il quale non piace a mia madre."
Does the Italian imply that my mother does not like the book, or that she does not like me not reading it? Or is it ambiguous like the translation?
It means my mother doesn't like the book I'm reading; if she didn't like me reading it instead of "il quale" it would have been "il che" or "la qual cosa".
Sono caduto una distanza lunga, la qual cosa era cattivo (I fell a long way which was bad) because the relative pronoun refers to the whole event described in the antecedent.
Yeah, but your example is a little off. Cadere is intransitive, so if you want to specify a length you should use 'per', but even then we usually use "da" specifying a height; when speaking about events, we don't use cattivo (we might sometimes use buono), and instead the adverbs bene/male; also, if you use "la qual cosa" (which feels more formal than "il che", same as "il quale" compared to "che") the adjective takes the gender of cosa. I would say "Sono caduto da molto in alto, il che è male" (I fell from a very high place, which is a bad thing).